Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Derivative [Line Items]
Derivative assets	$ 1,958.8		$ 1,958.8		$ 1,761.4
VM Convertible Senior Notes [Member]
Derivative [Line Items]
Interest rate	6.50%		6.50%
Cross-currency and interest rate derivative contracts
Derivative [Line Items]
Valuation adjustment in asset cross currency and interest rate derivative contracts	$ 63.3		$ 63.3		30.9
Valuation adjustment in liability cross currency and interest rate derivative contracts	155.4		155.4		64.6
Gain (loss) in changes in the credit risk valuation adjustments associated with our cross-currency and interest rate derivative contracts	77.2	$ (19.4)	60.3	$ (48.9)
Derivative assets	1,616.7		1,616.7		$ 1,357.3
Counterparty Credit Risk [Member]
Derivative [Line Items]
Derivative assets	$ 1,559.9		$ 1,559.9